This invention relates to a system for ascertaining the operational status of a pen in a vector plotter prior to a plotting operation and/or during intermediate stages of such an operation.
A significant amount of operational time of vector plotters is wasted as a result of attempting plots with inoperative pens either due to failure of the pen to be primed or clogging or other unsatisfactory conditions of the pens. Various proposals have been made for alleviating this problem including arrangements for priming a pen prior to a plotting operation (for example, U.S. Pat. No. 2,977,180 to Zenner and U.S. Pat. No. 4,782,349 to Sieber et al); storing the pen with the pen tip in a constantly wetted condition between plotting operations (for example, U.S. Pat. No. 3,613,248 to McInnis and U.S. Pat. No. 4,628,326 to Fukumura et al); removing excess ink, ink blobs, and clogs by the use of a felt or brush prior to a plotting operation (for example, U.S. Pat. No. 3,730,975 to Kono et al); and, providing optical means for detecting the failure of a pen to produce a desired line during a plotting operation and upon such detection causing the software to repeat the omitted portion of the line to correct the omission (for example, U.S. Pat. No. 4,335,674 to Hevenor et al). These proposed arrangements are unsatisfactory in that they either fail to confirm that the pen is in fact working or, in the case of Hevenor, only the failure of pen to produce a line during an actual plotting operation is detected with the consequent need to repeat portions of software controlling the portion of the plot where failure occurred. Additionally, in this latter case, the system for detecting failure of a pen during the actual plotting operation is complex and expensive.
Wherefore, it is an object of the present invention to provide a simple, economical system for ascertaining the operability of a pen immediately prior to or after a plotting operation thereby to overcome the shortcomings of the prior art and substantially reduce the waste and operational time lost in vector plotters as a result in attempting plotting operations with pens that are inoperative or operating unsatisfactorily.
Other objects and benefits of the invention will become apparent from the detailed description which follows hereinafter when taken in conjunction with the drawing figures which accompany it.